Hi Christian,
It all depends on your environment ...
Are you building SAPUI5 applications served from the JAVA stack of the NW portal ?
As an alternative you could indeed use the SAP JCO indeed to connect to an R/3 ABAP stack, execute the RFC and expose the results as a JSON HTTP result using eg a java HTTP servlet. I would reckon there might be quite some open source JSON java libraries available which would provide that information ... In this solution you would at least limit the custom developments on the ERP backends ... there simply needs to be a (custom) RFC available.
I reckon there should be plenty of tutorials on JCO development if you search on them on SDN.
The ABAP eclipse plugin is not required for any ABAP developments ... it can be an alternative for the standard SAP SE80 environment (so if you want to develop from within Eclipse ) ... and it is free of charge btw and can be downloaded via the normal SAP eclipse update sites ...
Regards,
Steven
